Method and apparatus for sensing moving ball

ABSTRACT

Provided are an apparatus and method for sensing a moving ball, which extract a feature portion such as a trademark, a logo, etc. indicated on a ball from consecutive images of a moving ball, acquired by an image acquisition unit embodied by a predetermined camera device, and calculate a spin axis and spin amount of rotation the moving ball based on the feature portion and thus spin of the ball is simply, rapidly, and accurately calculated with low computational load, thereby achieving rapid and stable calculation of the ball in a relatively low performance system. The sensing apparatus includes an image acquisition unit for acquiring consecutive images, an image processing unit for extracting a feature portion from the acquired image, and a spin calculation unit for calculating spin using the extracted feature portion.

CROSS REFERENCE TO PRIOR APPLICATION

This application is a Continuation of U.S. patent application Ser. No.14/759,654 filed Jul. 8, 2015, which is a National Stage Application ofPCT International Patent Application No. PCT/KR2014/000199 filed on Jan.8, 2014, under 35 U.S.C. § 371, which claims priority to Korean PatentApplication No. 10-2013-0002204 filed on Jan. 8, 2013, which are allhereby incorporated by reference in their entirety.

BACKGROUND

The present invention relates to a method and apparatus for sensing amoving ball for acquiring an image of the moving ball and processing andanalyzing the image to calculate the spin of the ball.

With regard to sports games, specifically, golf, attempts have alwaysbeen made to accurately sense the physical characteristics of a movingball that is hit by a golfer, to analyze the ball in flight or torealize the ball in flight in the form of an image using the sensedvalue, and to apply the result to simulated golf such as so-calledscreen golf.

In particular, when a ball is hit to fly, the ball rotates at very highspeed with respect to an axis in a three-dimensional space, and thus, itis very difficult to measure spin of the ball and very expensiveequipment is required to accurately measure the spin of the ball. Arepresentative method for measuring spin of a ball is a method using aradar sensor.

However, such an expensive sensing apparatus is not appropriate for ageneral-purpose sensing apparatus for analysis of a ball in flight inso-called screen golf or on a driving range, which senses a ball inflight according to golf swing, calculates a trajectory of the ball, andallows golf simulation on a virtual golf course based on the calculatedtrajectory. There is a need to a technology for rapidly and accuratelysensing spin of a ball also in a relatively inexpensive andlow-performance system.

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide anapparatus and method for sensing a moving ball, which extract a featureportion such as a trademark, a logo, etc. indicated on a ball fromconsecutive images of a moving ball, acquired by an image acquisitionunit embodied by a predetermined camera device, and calculate a spinaxis and spin amount of rotation the moving ball based on the featureportion and thus spin of the ball is simply, rapidly, and accuratelycalculated with low computational load, thereby achieving rapid andstable calculation of the ball in a relatively low performance system.

SUMMARY

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of an apparatus forsensing a moving ball, for acquiring and analyzing an image of themoving ball to calculate spin of the moving ball, the apparatusincluding an image acquisition unit for acquiring consecutive imagesaccording to movement of a ball with a surface having a predeterminedfeature portion indicated thereon, an image processing unit forextracting only a feature portion of a ball portion from each of imagesconsecutively acquired by the image acquisition unit, and a spincalculation unit for comparing and analyzing position information ofeach pixel of a feature portion obtained by applying a trial spin axisand a trial spin amount to position information of pixels constituting afeature portion of a ball portion on a first image as a preceding imageamong two consecutively acquired images of a moving ball, and positioninformation of each pixel constituting a feature portion of a ballportion of a second image as a subsequent image among the twoconsecutively acquired images, to calculate a spin axis and spin amountaccording to ball movement to the second image from the first image.

In accordance with another aspect of the present invention, there isprovided an apparatus for sensing a moving ball, for acquiring andanalyzing an image of the moving ball to calculate spin of the movingball, the apparatus including an image acquisition unit for acquiringconsecutive images according to movement of a ball with a surface havinga predetermined feature portion indicated thereon, an image processingunit for extracting a feature portion on a ball portion from each ofimages consecutively acquired by the image acquisition unit andextracting a feature portion from the ball portion to prepare a featureportion image of each of the consecutive images, and a spin calculationunit for calculating a spin axis and spin amount in a three-dimensionalspace to convert a feature portion image of a preceding image of twoconsecutive feature portion images into a feature portion image of asubsequently acquired image.

In accordance with another aspect of the present invention, there isprovided a method of sensing a moving ball, for acquiring and analyzingan image of the moving ball to calculate spin of the moving ball, themethod including acquiring consecutive images according to movement of aball with a surface having a predetermined feature portion indicatedthereon, extracting the feature portion indicated on one side of a ballportion of each of the consecutively acquired images, calculatingposition information of each pixel of a feature portion obtained byapplying a trial spin axis and a trial spin amount to positioninformation of pixels constituting a feature portion of a ball portionon a first image as a preceding image among two consecutively acquiredimages of a moving ball; and comparing and analyzing positioninformation of each pixel constituting a feature portion of a ballportion of a second image as a subsequent image among the twoconsecutively acquired images with the position information of each ofthe pixels of the feature portion obtained by applying the trial spinaxis and spin amount, to calculate a spin axis and spin amount accordingto ball movement to the second image from the first image.

In accordance with another aspect of the present invention, there isprovided a method of sensing a moving ball, for acquiring and analyzingan image of the moving ball to calculate spin of the moving ball, themethod including acquiring consecutive images according to movement of aball with a surface having a predetermined feature portion indicatedthereon, extracting a feature portion from a ball portion from each ofthe consecutively acquired images to prepare a feature portion image,and searching for a spin axis and spin amount in three-dimensionalspace, for allowing a feature portion image of a first acquired image oftwo consecutively acquired images into a feature portion image of asecond acquired image.

An apparatus and method for sensing a moving ball according to thepresent invention may extract a feature portion such as a trademark, alogo, etc. indicated on a ball from consecutive images of a moving ball,acquired by an image acquisition unit embodied by a predetermined cameradevice, and calculate a spin axis and spin amount of rotation the movingball based on the feature portion and thus spin of the ball is simply,rapidly, and accurately calculated with low computational load, therebyachieving rapid and stable calculation of the ball in a relatively lowperformance system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic block diagram illustrating a structure of anapparatus for sensing a moving ball according to an embodiment of thepresent invention;

FIG. 2 is a diagram for explanation of functions of components fromimage acquisition to calculation of spin of a ball using componentsillustrated in FIG. 1 ;

FIG. 3 is a diagram illustrating of a moving ball and two camerasconfigured in a stereo manner as an image acquisition unit according toan embodiment of the present invention;

FIGS. 4(a), 4(b), and 4(c) are source images of consecutively acquiredimages;

FIGS. 5(a), 5(b), and 5(c) are diagram for explanation of a procedure ofextracting a ball portion from the source image illustrated in FIGS.4(a), 4(b), and 4(c), respectively;

FIG. 6 is a diagram for explanation of an exemplary extraction methodfor extraction of a ball portion of FIG. 5 ;

FIGS. 7(a), 7(b), and 7(c) illustrate normalized images of extractedball images illustrated in FIGS. 5(a), 5(b), and 5(c), respectively;

FIGS. 8(a) and 8(b) are normalized images of ball images extracted fromtwo consecutive source images, respectively, and FIGS. 8(c) and 8(d)illustrate feature portion images extracted from the images illustratedin FIGS. 8(a) and 8(b);

FIG. 9 is a diagram for explanation of calculation of spin of a movingball;

FIGS. 10 and 11 are diagrams for explanation of a principle forcorrecting a position and direction of a camera for calculation of spinof a ball; and

FIG. 12 is a flowchart for explanation of a method of sensing a movingball according to an embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of a method and apparatus for sensinga moving ball according to the present invention will be described indetail with reference to the accompanying drawings.

The present invention may be basically configured to photograph a golfball (hereinafter, referred to as a “ball”), which is hit by a golf clubof a user, via a predetermined camera, to analyze the captured image,and to calculate spin of the ball in flight. Here, the camera may be athree-dimensional camera or a stereo camera configured by a plurality ofcameras in a stereo manner and may be configured to convert coordinatesof a two-dimensional image of the ball into three-dimensionalcoordinates or vice versa.

In addition, the method and apparatus for sensing a moving ballaccording to the present invention may be applied to various fields suchas analysis of a ball in flight according to golf swing of a user, avirtual golf using a virtual reality-based simulation, and so on.

First, an apparatus for sensing a moving ball according to an embodimentof the present invention will be described with reference to FIGS. 1 and2 .

As illustrated in FIGS. 1 and 2 , an apparatus for sensing a moving ballaccording to an embodiment of the present invention includes an imageacquisition unit 100, an image processing unit 200, and a spincalculation unit 300.

The image acquisition unit 100 may be a camera device and may beembodied through a three-dimensional camera device or a stereo cameraincluding a plurality of cameras, as described in the background art.FIG. 1 illustrates a case in which the image acquisition unit 100 isembodied as a stereo camera device including a first camera 110 and asecond camera 120.

The image processing unit 200 is a component that extracts a ball imagethat is an image corresponding to a ball portion from each imageacquired by the image acquisition unit 100 and removes a dimple portionand various noise portions from the ball image to extract a featureportion of the ball image, that is, an unspecified indication such as atrademark or a logo indicated on the ball, a scratch, etc.

The image processing unit 200 may include a ball image extraction part210 and a ball feature extraction part 230.

The ball image extraction part 210 is configured to extract a ball imagethat is an image corresponding to a ball portion from a source imagethat is an image acquired by the image acquisition unit 100 and toextract a central coordinate of the ball portion, which will bedescribed below in detail.

The ball feature extraction part 230 is a component that normalizessize, brightness, and so on of each ball image extracted by the ballimage extraction part 210 and extracts the feature portion (i.e., anunspecified indication such as a trademark or a logo indicated on theball, a scratch, etc.) indicated on the image, which will be describedbelow in detail.

The spin calculation unit 300 is configured to analyze a position changein feature portions that are respectively extracted from two consecutiveball images, that is, to analyze a spin axis and spin amount in apredetermined three-dimensional space, by which a feature portion of apreceding image is converted into a feature portion on a subsequentimage to calculate final spin axis and spin amount information of theball. As illustrated in FIGS. 1 and 2, the spin calculation unit 300includes a position correction part 310, a spin applying part 320, and aspin determination part 330.

The position correction part 310 facilitates spin calculation when ballsin two consecutive images are viewed at corresponding positions and thesame angle for spin calculation of a ball to accurately calculate spin,which will be described below in detail.

According to the present invention, analysis is basically performed inunits of images among images of a consecutively photographed movingball. When a preceding image is referred to as a first image and asubsequent image is referred to as a second image, spin when a ballstate of a point for acquisition of the first image is converted into aball state of a point for acquisition of the second image may becalculated and, in detail, may be calculated using a method ofcalculating a spin axis and spin amount for allowing a position of afeature portion in the first image to be converted into a position of afeature portion of the second image.

The spin applying part 320 extracts and applies trial spin axis and spinamount information in order to calculate the spin axis and spin amountfor allowing the position of the feature portion on the first image tobe converted into the position of the feature portion of the secondimage. Thus, the spin determination part 330 may determine whether thetrial spin axis and spin amount information applied by the spin applyingpart 320 are close to target spin axis and spin amount information tocalculate final spin information.

That is, until the final spin information is calculated, the spinapplying part 320 extracts and applies a trial spin axis and a trialspin amount every time, and the spin determination part 330 checks theapplication result and determines the most appropriate trial spininformation as final spin information, which will be described below indetail.

As illustrated in FIG. 3 , position information may be obtained atpositions where ball images are respectively acquired by the firstcamera 110 and the second camera 120 according to movement of a ball 10from the ball images based on an i, j, and k coordinate system of aground surface G.

That is, the first camera 110 and the second camera 120 may each be animage acquisition device having a stereoscopic configuration, and thus,may extract three-dimensional coordinate information of an object fromimages acquired by photographing the same object via two cameras, i.e.,the first camera 110 and the second camera 120. In FIG. 3 , as the ball10 moves from a first position to a second position, coordinateinformation (x, y, z) of the first position and coordinate information(x′, y′, z′) of the second position may be extracted. In this case, thefirst camera 110 and the second camera 120 are fixed. Accordingly,position coordinates of the first camera 110 and the second camera 120may be recognized and may always be fixed.

In this state, some of consecutively acquired images of any one cameraare illustrated in FIGS. 4(a), 4(b), and 4(c).

That is, FIGS. 4(a), 4(b), and 4(c) illustrate images in states in whichonly ball portions 21, 22, and 23 remain by removing a backgroundportion and so on using a differential image from images acquired byphotographing a moving ball within a viewing angle via a fixed camera ata predetermined time interval.

As seen from FIGS. 4(a), 4(b), and 4(c), a current state is a state inwhich a ball flies in a left diagonal direction. As seen from FIGS.4(a), 4(b), and 4(c), when the ball approaches a camera, the viewed ballis enlarged like the ball portion 21 as illustrated in FIG. 4(a), andthen, as the ball gradually moves away from the camera, the viewed ballbecomes smaller like the ball portions 22 and 23 as illustrated in FIGS.4(b) and 4(c).

Here, the images illustrated in FIGS. 4(a), 4(b), and 4(c), that is, animage of a ball portion as a moving portion, remaining after removal ofa background portion and various noise portions from an initiallyacquired image via a differential image, etc., is referred to as asource image.

With regard to the ball portions 21, 22, and 23 on the source image,positions of feature portions F1, F2, and F3 indicated on a surface ofthe ball change as the ball rotates.

Here, interest objects are the feature portions F1, F2, and F3 on theball. In this regard, the feature portions F1, F2, and F3 may beaccurately extracted and a position change of the feature portions F1,F2, and F3 may be analyzed to calculate spin of the ball.

To this end, it is necessary to effectively extract only images of theball portions 21, 22, and 23, that is, only a ball image from the sourceimage, as illustrated in FIG. 4 .

FIGS. 5(a), 5(b), and 5(c) illustrate a procedure of extracting only aball portion from each source image. First, the ball portions 21, 22,and 23 may be accurately extracted from source images such that acentral point C of the ball portion 21 is a central portion of anextracted ball image 211 and an outline of the ball portion 21substantially corresponds to an outline of the extracted image 211 asillustrated in FIG. 6 .

Images obtained by extracting only the ball portions 21, 22, and 23 fromthe respective source images, that is, ball images 211, 212, and 213have sizes corresponding to ball portions on the respective sourceimages, and thus, have different sizes. The ball images 211, 212, and213 indicated in the respective source images are differently affectedby illumination according to a distance from a camera, and thus,brightness also varies for each respective ball image.

In order to accurately extract a ball feature portion, it is necessaryto equalize the sizes of the ball images 211, 212, and 213 and normalizethe brightness of the ball images 211, 212, and 213.

FIGS. 7(a), 7(b), and 7(c) illustrate images containing ball imagescorresponding to FIGS. 5(a), 5(b), and 5(c), the size and brightness ofwhich are normalized.

That is, the ball images 211, 212, and 213 may be enlarged or reducedaccording to respective preset sizes or remaining ball images may beenlarged or reduced based on any one of the ball images 211, 212, and213, that is, a normalization process may be performed on each ballimage, thereby equalizing the sizes of ball images 211, 212, and 213.

In addition, a normalization process may be performed on each ball imageusing an average value of all pixels constituting a ball portion toequalize overall brightnesses of ball images.

As described above, after normalization is completed on each ball image,extraction of a ball feature portion using a ball feature extractionpart is performed on each normalized ball image, as illustrated in FIG.8 .

That is, when a ball image of FIG. 8(a) is a first ball image and a ballimage of FIG. 8(b) is a second ball image, the first ball image is afirst acquired image of two consecutively acquired images and the secondball image is a second acquired image of the two images. FIG. 8(c)illustrates a first feature portion image having a feature portion FC1obtained by completely extracting the feature portion F1 from the firstball image. FIG. 8(d) illustrates a second feature portion image havinga feature portion FC2 obtained by completely extracting the featureportion F2 on the second ball image.

Here, the feature portion may be extracted using various imageprocessing schemes such as a differential image scheme and so on.

When feature portion images having the extracted feature portions FC1and FC2 are prepared, a procedure of calculating spin information of amoving ball is performed using a spin calculation unit.

Here, the spin of the ball may be calculated by calculating coordinateinformation about a spin axis in a three-dimensional space based on ani-axis, j-axis, and k-axis coordinate system and an angle for rotationwith respect to the spin axis, that is, information about a spin amount,as illustrated in FIG. 9 .

As illustrated in FIG. 9 components for representing rotational motionin three-dimensional space include pitch, yaw, and roll (for example,when a spin axis corresponds to a k axis, a ball has only side spin, andwhen the spin axis corresponds to an i axis, the ball has only back spinor forward spin). In addition, when a rotational component in an i-axisdirection is θ, a rotational component in a j-axis direction is λ, and arotational component in a k-axis direction is ρ, a vector of target spinmay be represented according to Equation 1 below.{right arrow over (ω)}=θi+λj+ρk  [Equation 1]

Based on the spin vector (ω), the spin axis information and the spinamount information may be calculated according to Equations 2 and 3below, respectively. Here, α is the spin amount information.

$\begin{matrix}{\hat{\omega} = ( {\frac{\theta}{\alpha},\frac{\lambda}{\alpha},\frac{\rho}{\alpha}} )} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack \\{\alpha = \sqrt{\theta^{2} + \lambda^{2} + \rho^{2}}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

Accordingly, the spin axis and spin amount information may be obtainedby calculating θ as a yaw rotational component of spin of a moving ball,λ as a roll rotational component, and ρ as a pitch rotational component.

The spin axis and spin amount information may be obtained from a featureportion extracted from the ball image shown in FIG. 7 .

That is, as illustrated in FIG. 8 , the spin axis and spin amount may beextracted using feature portion images (FIGS. 8(c) and 8(d)) of twoconsecutive ball images.

To this end, first, it is necessary to correct position information ofeach pixel constituting the feature portion.

That is, with regard to positions of a ball on an image acquired by acamera, a spin axis and spin amount are differently viewed according toa direction in which the camera is directed, and thus, it is necessaryto accurately establish a reference and to calculate an absolute spinaxis and spin amount based on the reference. To this end, position anddirection information of the camera may be corrected as if respectiveballs on consecutively acquired images are viewed at the same positionand direction with respect to the camera, thereby accurately calculatingspin information of the ball.

FIGS. 10 and 11 are diagrams for explanation of a principle of theaforementioned position correction.

The sensing apparatus and method according to the present inventioncalculates spin information from position change of a feature portion oftwo consecutive images. In order to accurately calculate the spininformation, a pair of consecutive images needs to be viewed at the sameposition and direction. That is, it is necessary to correct consecutiveacquired images as if respective balls on the images are viewed at thesame position and direction with respect to the camera while the cameramoves together with the ball (a passing ball is always photographed by afixed camera).

As an example for establishing references of a position and direction ofthe camera, as illustrated in FIG. 10 , when the ball 10 moves in adirection d, a direction Bi that is a vector component in parallel tothe ground surface G and is contained in a plan p orthogonal to a vectorcomponent Bj corresponding to a direction in which the ball 10 proceedsmay be established as a reference.

That is, as illustrated in FIG. 11 , it is necessary to generateposition correction information for correction of the position anddirection of a camera 110 and to apply the position correctioninformation to spin calculation as if ball images acquired by the camera110 are viewed in a direction of the direction vector Bi that isparallel to the ground surface G and perpendicular to the directionvector Bj in which the ball 10 moves for each respective position.

The position correction may be achieved by correcting an angle at whicha ball is viewed with respect to a camera, using coordinate informationof a fixed camera and central coordinate information of the ball, whichare already known. The position correction may be achieved by applyinginformation about a portion to be corrected to position coordinates ofpixels each extracted feature portion instead of actually correcting animage.

Position information of each pixel constituting the first featureportion FC1 (refer to FIG. 8 ) is converted into three-dimensionalposition information, a resulting value is obtained by applying theaforementioned position correction information and applying trial spinaxis and spin amount to the three-dimensional position information, andthen, the resulting information is re-converted into two-dimensionalposition information.

Comparing the converted two-dimensional position information with theposition information of pixels constituting the second feature portion,when the converted two-dimensional position information corresponds tothe position information of pixels constituting the second featureportion, the applied trial spin axis and spin amount information may beaccurate target spin axis and spin amount information.

Accordingly, as described above, the sensing apparatus and methodaccording to the present invention may repeatedly apply trial spin axisand spin amount information to obtain position information and may findspin axis and spin amount information that correspond to the obtainedposition information at a predetermined level or more to calculate finalspin information.

This is represented according to the following equations.

This may be represented by converting position information of pixelsconstituting each of the first and second feature portions intothree-dimensional position information according to Equations 4 and 5below.PC1set_3D=C1*P1set_3D  [Equation 4]PC2set_3D=C2*P2set_3D  [Equation 5]

In Equations 4 and 5, P1set_3D is a matrix obtained by converting P1 setinto three-dimensional coordinate information, where P1set is a matrixof coordinates (two-dimensional coordinates) of each pixel on the firstfeature portion FC1 (refer to FIG. 8 ).

P2set_3D is a matrix obtained by converting P2set into three-dimensionalcoordinate information, where P2set is a matrix of coordinates(two-dimensional coordinates) of each pixel on the second featureportion FC2 (refer to FIG. 8 ).

C1 and C2 are rotation matrices calculated as position correctioninformation according to the principle illustrated in FIGS. 10 and 11 ,C1 is for correction of position coordinates of pixels of the firstfeature portion, and C2 is for correction of position coordinates ofpixels of the second feature portion.

PC1set_3D is a matrix obtained by correcting positions ofthree-dimensional coordinates of the pixels of the first feature portionand PC2set_3D is a matrix obtained by correcting positions ofthree-dimensional coordinates of the pixels of the second featureportion.

When a spin axis vector as target final spin information is ω and a spinamount is α, a rotation matrix R(ω, α) may be calculated using ω and α.A correlation of R(ω, α), and PC1set_3D and PC2set_3D that are obtainedby converting positions of pixels of the respective feature portionsinto three-dimensional coordinate information satisfies Equation 6below.R(ω,α)*PC1set_3D=PC2set_3D  [Equation 6]

Equations 4 and 5 above may be substituted into Equation 6 above toobtain a correlation represented in Equation 7 below.PC2set_3D=C2T*R(ω,α)*C1*P1set_3D  [Equation 7]

Here, C2T is transposition of matrix C2.

According to Equation 7 above, position information of the pixels of thefirst feature portion may be converted into three-dimensional positioninformation, and a resulting value may be obtained by applying positioncorrection information and applying trial spin information to thethree-dimensional position information. That is, trial spin informationmay be substituted into R(ω,α) as target final spin information inEquation 7 above.

When Tset_3D is a result obtained by substituting a rotation matrixR(ω′,α′) calculated using a trial spin axis vector ω′ and a trial spinamount α′ as trial spin information into Equation 7 above, Equation 8below is satisfied.Tset_3D=C2T*R(ω′,α′)*C1*P1set_3D  [Equation 8]

When Tset is obtained by converting Tset_3D calculated according toEquation 8 above into a two-dimensional coordinate, if Tset and P2setcorrespond to each other, R(ω′,α′) and R(ω,α) have the same value, andthus, R(ω′,α′) as the trial spin information R(ω′,α′) may be determinedas final spin information.

That is, trial spin information applied to Tset closest to P2set, thatis, having highest similarity among a plurality of Tset to whichdifferent trial spin information is applied may be determined as thefinal spin information.

That is, if Tset and P2set are compared and the number of pixels havingcorresponding position coordinates is calculated, when the number of thecorresponding pixels is equal to or greater than a predetermined level,or if similarity between pixels of Tset and pixels of P2set iscalculated according to a predetermined function is equal to or greaterthan a predetermined level, trial spin information applied to thecorresponding Tset is final spin information.

Here, the similarity may be determined, for example, based on a ratio ofthe number of the corresponding pixels to all pixels.

The aforementioned procedure of calculating spin of a moving ball willbe described with reference to a flowchart of FIG. 12 .

First, consecutive images of a moving ball are acquired (S10) and abackground portion and so on are removed from each of the acquiredimages to extract respective source images (S12).

In addition, a ball portion is found from each source image to extractball images (S20) and a ball feature portion is extracted from each ofthe ball images to prepare respective feature portion images (S30).

When a preceding image of two images among the consecutive featureportion images is referred to as a first feature portion image and asubsequent image of the two images is referred to as a second featureportion image, spin may be calculated using position information ofpixels constituting the first feature portion on the first featureportion image and position information of pixels constituting the secondfeature portion on the second feature portion image.

That is, the position information of pixels constituting the firstfeature portion is converted into three-dimensional position information(S42) and position correction information is applied to thethree-dimensional position information (S44).

In addition, a trial spin axis and a trial spin amount are extracted andapplied to the three-dimensional position information (S52) and thethree-dimensional position information is re-converted intotwo-dimensional position information (S54).

The two-dimensional position information converted in operation S54 iscompared with the position information of the pixels constituting thesecond feature portion (S62). When the number of pixels havingcorresponding position coordinates is calculated, if the number is equalto or greater than a preset number (S64), the applied trial spin axisand spin amount is determined as a final spin axis and spin amount(S72).

When the calculated “number of corresponding pixels” does not reach apreset number, other trial spin axis and spin amount are applied torepeat operations S52, S54, S62, S64, and so on, a trial spin axis and atrial spin amount is determined as the final spin axis and spin amountwhen the “number of corresponding pixels” is highest.

Here, the flowchart of FIG. 12 illustrates the case in which a trialspin axis and a trial spin amount are finally selected when the “numberof corresponding pixels” is equal or greater than a preset number.However, the present invention is not limited thereto. For example, apreset number may not be present with respect to the “number ofcorresponding pixels”, different trial spin information may berepeatedly applied, and trial spin information may be finally selectedwhen the “number of corresponding pixels” is highest.

In addition, instead of selecting final spin information through thenumber of pixels, similarity may be calculated according to a functionand the final spin information may be selected according to thesimilarity.

Consideration of all of a pitch rotational component, a yaw rotationalcomponent, and a roll rotational component for applying a trial spinaxis, as illustrated in FIG. 9 may mean consideration of significantlygreat number for extraction of trial spin axis and spin amount.Accordingly, a limited range for the trial spin axis may be reasonablyset. Also, a limited range for a trial spin amount may also bereasonably set for applying the trial spin amount. Then, trial spin axisand spin amount information may be extracted mainly within the limitedranges to drastically reduce the number of cases to be considered and tosignificantly reduce computational load, thereby rapidly calculatingspin.

That is, limited conditions for extraction a trial spin axis and a trialspin amount may be set in consideration of the characteristics of ballmovement and a frame rate of a camera, thereby rapidly calculating spin.

When a golf ball is hit by a golf club, a pitch rotational component anda yaw rotational component are strongly represented among threerotational component of spin and a roll rotational component is notpresent or is almost negligible, as illustrated in FIG. 9 .

That is, when the golf ball is hit, right and left side spin and forwardand reverse spin are realized and a roll rotational component based on aproceeding direction of a ball is not present or is almost negligible.

Accordingly, a trial spin axis may be selected in consideration of onlya pitch rotational component and a yaw rotational component whiledisregarding a roll rotational component to some extent, and thus, thenumber of cases to be considered may be significantly reduced.

When the golf ball is hit by the golf club, there is a limit in arotation degree from a ball state of a captured image of one frame to aball sate of a captured image of a subsequent frame.

That is, since there is a limit in maximum spin for rotation accordingto user hit and there is a limit in a frame rate of a camera forcapturing an image, the number of cases to be considered for a trialspin amount may be largely limited.

Accordingly, as described above, limited ranges for a trial spin axisand a trial spin amount may be preset to reduce computation load,thereby rapidly calculating spin.

Thus far, the procedure of calculating spin information about only twoimages among consecutively acquired images has been described.Alternatively, several tens of frames to several thousands of frames maybe acquired per second according to a camera, and the aforementionedspin calculation procedure may be performed on all of a plurality ofconsecutive images or some of the consecutive images only.

That is, the aforementioned spin calculation procedure may be performedon a plurality of pairs, each of which includes a preceding image and asubsequently acquired image of two consecutive images to obtain aplurality of spin information. The plural spin information may beslightly different and may be collected according to a preset function(for example, extraction of an average value or extraction of an averagevalue of only several values with high similarity) to calculate finalspin information, or spin information with highest similarity among thecalculated plural spin information may be selected as the final spininformation.

Various embodiments have been described in the best mode for carryingout the invention.

A method and apparatus for sensing a moving ball according to thepresent invention is applicable to an industrial field related to golftraining including analyzing a ball in flight according to golf swing, aso-called screen golf industrial field providing a virtual reality-basedsimulation to allow a user to play a virtual golf game, and so on.

What is claimed is:
 1. A method of sensing a moving ball, for acquiringand analyzing an image of the moving ball to calculate spin of themoving ball, the method comprising: acquiring consecutive images by animage acquisition unit according to movement of a ball with a surfacehaving a predetermined feature portion indicated thereon, wherein thefeature portion is an unspecified indication including a ball'strademark or a logo and a scratch on the ball; preparing a first imageand a second image consecutively acquired by the image acquisition unit;finding a ball portion on the first image and extracting the ballportion having a predetermined size from the first image as a first ballimage; finding a ball portion on the second image and extracting theball portion having the predetermined size from the second image as asecond ball image; extracting the feature portion of the ball from thefirst ball image to prepare a first feature portion image; extractingthe feature portion of the ball from the second ball image to prepare asecond feature portion image; converting position information of eachpixel on the first feature portion image into 3D position information,applying a trial spin axis and a trial spin amount to the converted 3Dposition information, and re-converting the 3D position information towhich the trial spin axis and the trial spin amount have been appliedinto 2D position information, wherein the re-converted 2D positioninformation is prepared as a trial spin feature portion; and comparinginformation of the trial spin feature portion with information of thesecond feature portion image to calculate a similarity, and determiningthe trial spin axis and the trial spin amount corresponding to the trialspin feature portion as a final spin axis and spin amount according tothe similarity between information of the trial spin feature portion andinformation of the second feature portion image, wherein the methodfurther comprises calculating position correction information forcorrecting a position and direction of a camera as if respective ballson consecutively acquired images are viewed at the same position anddirection with respect to the camera, wherein the position correctioninformation is applied to the converted 3D position information to applythe trial spin information and to calculate spin information.
 2. Amethod of sensing a moving ball, for acquiring and analyzing an image ofthe moving ball to calculate spin of the moving ball, the methodcomprising: acquiring consecutive images by an image acquisition unitaccording to movement of a ball with a surface having a predeterminedfeature portion indicated thereon, wherein the feature portion is anunspecified indication including a ball's trademark or a logo and ascratch on the ball; preparing a first image and a second imageconsecutively acquired by the image acquisition unit; finding a ballportion on the first image and extracting the ball portion having apredetermined size from the first image as a first ball image; finding aball portion on the second image and extracting the ball portion havingthe predetermined size from the second image as a second ball image;extracting the feature portion of the ball from the first ball image toprepare a first feature portion image; extracting the feature portion ofthe ball from the second ball image to prepare a second feature portionimage; searching for a trial axis and a trial spin amount in 3D space,for allowing the first feature portion image into the second featureportion image; converting position information of each pixel on thefirst feature portion image into 3D position information, applying thesearched trial spin axis and the searched trial spin amount to theconverted 3D position information, and re-converting the 3D positioninformation to which the trial spin axis and the trial spin amount havebeen applied into 2D position information, wherein the re-converted 2Dposition information is prepared as a trial spin feature portion; andcomparing information of the trial spin feature portion with informationof the second feature portion image to calculate the number ofcorresponding pixels between information of the trial spin featureportion and information of the second feature portion image; anddetermining the trial spin axis and the trial spin amount correspondingto the trial spin feature portion as a final spin axis and spin amountinformation according to the number of corresponding pixels betweeninformation of the trial spin feature portion and information of thesecond feature portion image, wherein the method further comprisescalculating position correction information for correcting a positionand direction of a camera as if respective balls on consecutivelyacquired images are viewed at the same position and direction withrespect to the camera, wherein the position correction information isapplied to the converted 3D position information to apply the trial spininformation and to calculate spin information.
 3. The method accordingto claim 2, wherein the trial spin axis information applied to theconverted three-dimensional position information comprises spin amountinformation arbitrarily selected from a preset range according tomaximum spin limitation for rotation by user hit and a frame rate of acamera for capturing an image.
 4. The method according to claim 2,wherein the searching for of the spin axis and the spin amount comprisescollecting based on a predetermined function a plurality of spininformation calculated by performing the step of applying trial spininformation, the step of comparing position information, and the step ofdetermining the spin axis and spin amount of the trial spin informationas final spin axis and spin amount for each of a plurality of pairs,each pair of images comprising a preceding one and a later one of twoconsecutive images to calculate the spin information of the moving ball.